File directory structures, in particular hierarchical file directory structures, are used inter alia for organizing individual files within a large dataset which is held on a hard disk of a computer, for example, and for finding said files again. A typical example is, for example, the Microsoft® software application Windows Explorer
Furthermore, internet technologies such as HTTP, for example, providing the ability to communicate using internet browsers such as Internet Explorer® browser software or Netscape® browser software, for example, are increasingly found in the world of automation engineering. This applies particularly in the field of embedded systems. Embedded systems or embedded devices are understood to be systems with embedded computer functions, such as those which are found in e.g. intelligent sensors and actuators, bus modules, and in many device and machine controllers and in other applications of automation engineering. A range of Web servers is also now available for the field of embedded systems, thereby allowing the automation devices to communicate as appropriate with or via internet/intranet.
All of these Web servers for embedded systems essentially have the same problems. On the one hand, there are limited resources on the target machine or on the automation device concerned, and therefore a file system or a file directory structure is normally absent. Since objects which need to be addressed using internet technologies are addressed by means of a so-called URL (Uniform Resource Locator), and these URLs use a hierarchical structure for addressing as provided by file systems, objects that are located on such embedded systems cannot be readily addressed. On the other hand, however, there is a requirement for remote access to these automation devices or embedded systems, since they normally operate at a distance and are unattended. Remote operation or remote configuration, e.g. in the event of errors, for maintenance purposes, etc., can reduce the presence of personnel on site and is therefore cost-effective. In order to satisfy this requirement, file systems are now being post-implemented at considerable cost, and files then exist as independent storage blocks, for example, which have to be managed e.g. via the so-called FTP service (File Transfer Protocol). In addition to the problem that the management of such individual storage blocks is very burdensome, it is normally also necessary additionally to implement such an FTP server on the embedded system, thereby further reducing the resources on the target machine. Moreover, automation systems which are protected by firewalls are not necessarily open to an FTP server, and remote access is therefore obstructed in some cases.
WO 01 18633 A discloses a system and a method for securely storing and reliably transferring information, and for reliably accessing information using a computer. An algorithm is used for generating a unique identifier (Intrinsic Unique Identifier—IUI) for a file, wherein said identifier is also used for encrypting and decrypting the file. It is proposed to store the unique identifiers of various files together with metadata relating to the files, e.g. file names and file attributes, in a descriptor file. Directory structures can also be represented.